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\(\left(\frac{2121}{1212}+\frac{2121}{2020}+\frac{2121}{3030}+\frac{2121}{4242}\right)-x=-2015\)
\(\left(\frac{21}{12}+\frac{21}{20}+\frac{21}{30}+\frac{1}{2}\right)=-2015+x\)
\(\left(\frac{7}{3}+\frac{21}{20}+\frac{7}{10}+\frac{1}{2}\right)=-2015+x\)
\(\left(\frac{140}{60}+\frac{63}{60}+\frac{42}{60}+\frac{30}{60}\right)=-2015+x\)
\(\frac{275}{60}=-2015+x\)
\(\frac{55}{12}+2015=x\)
\(x=\frac{55}{12}+\frac{24180}{12}\)
\(x=\frac{24235}{12}\)
\(=\frac{2002}{12}+\frac{2002}{20}+\frac{2002}{30}+\frac{2002}{42}+\frac{2002}{56}\)
\(=2002.\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\right)\)
\(=2002.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\right)\)
\(=2002.\left(\frac{1}{3}-\frac{1}{8}\right)\)
\(=2002.\frac{5}{24}\)
\(=\frac{5005}{12}\)
35/49=5/7 ;5/8 ;36/56=9/14 ;57/63=19/21 ;2020/2121=20/21;
5/7 ;5/8 ;9/14 ;19/21 ;20/21
MSC:168
5/7=120/168
5/8=105/168
9/14=108/168
19/21=152/168
20/21=160/168
Vì:160/168>152/168>120/168>108/168>105/168
Nên:20/21>19/21>5/7>9/14>5/8
Vậy:\(\frac{2020}{2121}\)>\(\frac{57}{63}\)>\(\frac{35}{49}\)>\(\frac{36}{56}\)>\(\frac{5}{8}\).
\(\frac{2020}{2121}<\frac{5}{8}<\frac{36}{56}<\frac{35}{49}<\frac{57}{63}\)
B=(1-\(\frac{1}{2}\))x(1-\(\frac{1}{3}\))x(1-\(\frac{1}{4}\))x...x(1-\(\frac{1}{20}\))
B=\(\frac{1}{2}\)X\(\frac{2}{3}\)X\(\frac{3}{4}\)X...X\(\frac{19}{20}\)
B=\(\frac{1.2.3.4.4.5.7.8.9.10.11.12.13.14.15.16.17.18.19}{2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20}\)
B=20
Vậy B=20
Không biết kết quả đúng ko nhưng cách làm thì đúng.
B= \(\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x...x\left(1-\frac{1}{20}\right)\)
=\(\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.....\frac{19}{20}\)(Rút gọn cả tử xuống mẫu )
= \(\frac{1.2.3...19}{2.3.4...20}\)
=\(\frac{1}{20}\)
Vậy B= \(\frac{1}{20}\)
\(\frac{1414+1515+1616+1717+1818+1919}{2020+2121+2222+2323+2424+2525}\)
\(=\frac{101\left(14+15+16+17+18+19\right)}{101\left(20+21+22+23+24+25\right)}\)
\(=\frac{\left(19+14\right)\left(19-14+1\right):2}{\left(25+20\right)\left(25-20+1\right):2}\)
=\(\frac{33.6:2}{45.6:2}=\frac{33}{45}=\frac{11}{15}\)
\(a,\frac{1995}{1996}.\frac{19961996}{19311931}.\frac{193119311931}{199519951995}\) \(c,\frac{1997.1996-1}{1995.1997+1996}\)
\(=\frac{1995}{1996}.\frac{1996}{1931}.\frac{1931}{1995}\) \(=\frac{1997.\left(1995+1\right)-1}{1995.1997+1996}\)
\(=\frac{1995.1996.1931}{1996.1931.1995}\) \(=\frac{1997.1995+1997-1}{1997.1995+1996}\)
\(=1\) \(=\frac{1997.1995+1996}{1995.1997+1996}\)
\(=1\)
Ý (a) giống ý (b)
Ý (c) giống ý (d)
\(\frac{42}{46}+\frac{250}{186}+\frac{-2121}{2323}+\frac{-125125}{143143}\Leftrightarrow\frac{21}{23}+\frac{125}{93}+\frac{-21}{23}+\frac{-125}{143}\)
\(\Rightarrow\left(\frac{21}{23}+\frac{-21}{23}\right)+\left(\frac{125}{93}+\frac{-125}{143}\right)=\frac{17000}{3999}\)
B1:
\(\frac{42}{46}+\frac{250}{186}+\frac{-2121}{2323}+\frac{-125125}{143143}\)
=\(\frac{21}{23}+\frac{125}{143}+\frac{-21}{23}+\frac{-125}{143}\)
=\(\left(\frac{21}{23}+\frac{-21}{23}\right)+\left(\frac{125}{143}+\frac{-125}{143}\right)\)
=0+0=0
làm một câu thôi nha :33
Chúc bạn học tôt!
=>(\(\frac{7}{4}+\frac{21}{20}+\frac{7}{10}+\frac{1}{2}\))-x=-2015
=>(1,75+1,05+0,7+0,5)-x=-2015
=>4-x=-2015
=>x=4-(-2015)
=>x=2019
(\(\frac{2121}{1212}+\frac{2121}{2020}+\frac{2121}{3030}+\frac{2121}{4242}\)) - x = -2015
=> ( \(\frac{21}{12}+\frac{21}{20}+\frac{21}{30}+\frac{21}{42}\) ) - x = -2015
=> ( \(\frac{7}{4}+\frac{21}{20}+\frac{21}{30}+\frac{1}{2}\) ) - x = -2015
=> ( 1,75 + 1,05 + 0,7 + 0,5 ) - x = -2015
=> 4 - x = -2015
=> x = 4 - ( -2015 )
=> x = 4 + 2015
=> x = 2019